Sexual reproduction among the higher and lower representatives of the flora

Reproduction is characteristic of all organisms. This ability to reproduce provides continuity and continuity of life. In organisms that have a cellular form of structure, division is the basis of reproduction.

Different scientists have proposed different classifications of reproduction types. The main types of reproduction are: vegetative, sex and asexual.

In the latter case, the development of the organismis carried out from one cell, not sexually differentiated. Vegetative reproduction is characterized by the development of the organism from multicellular embryos, sometimes difficult to differentiate.

Sexual reproduction of plants begins withthe formation of sex cells (gametes). Reproduction itself boils down to the fusion of gametes into a zygote. This process is called fertilization and provides the transfer of genetic data from parents to offspring.

Gametes are formed in the genital organs - gametangia. Representatives of the flora, which are characterized by fertilization, have a meiosis in their development cycle.

Sexual reproduction is not typical for blue-green algae, bacteria. This method of reproduction is not found in a number of fungi.

Types of sexual reproduction in the lower representativesflora are different. Thus, in some green algae, the process of reproduction can occur without the formation of gametes. In this case, two unicellular organisms merge.

The fusion of gametes that have flagella is called isogamy. Such sexual reproduction is characteristic of many algae.

Single-celled algae (some chlamydomonads,for example) to some extent themselves turn into genital organs, forming gametes. Multicellular representatives of gametangiae become separate cells, not differing from others, or gametangia are formed, which have morphological differences (for example, in the ectocarpus).

For many isogamous algae, heterogarallism (genetic and physiological sexual separation) is characteristic. In this case, a fusion of physiologically different gametes occurs.

For some algae, conjugation is characteristic: a "flow" of protoplast from one cell to another takes place.

The fusion of gametes of different sizesflagellum, is called heterogamy. The connection of an unbuttoned female gamete (egg) and having flagella (most often) of a small male (sperm) is called oogamy. Such sexual reproduction is typical for many red, brown, diatomaceous, green algae, as well as a number of lower fungi.

Fertilization in the hologram, heterogamous,isogamous and most oogamous representatives of the flora is carried out in the water. In a number of oogamous plants, the fusion process takes place in oogonia (female gametangia). They are actively promoted by spermatozoa released into the water. Activity, apparently, is due to chemotaxis. In this spermation of red squids (red algae) are moved by a current of water - passively.

Higher plants are oogamous. However, their fertilization takes place in different ways. For higher plants, multicellular gametangia are typical - archegonia (female) and antheridia (male). In the outer layer of the genital organs, the cells are sterile. In archegonium, egg cells are formed one by one, in antheridia, spermatozoa are usually formed in large numbers.

Sexual reproduction of fern-like andBryophytes are carried in water. The spermatozoa leave the antheridia and move towards the archegonia. In turn, ready-to-fertilize archegonia attract spermatozoa by excreting mucus from the exposed top. Moving on in the mucus, the spermatozoa approach the egg, but merges with it alone.